Rotary hearth furnaces (RHF) are used for reduction of iron oxides in agglomerates containing iron ore or waste oxides with carbonaceous reductant in steel plants. The largest one RHF currently under construction for ironmaking from iron ores in Thailand represents the best available technology for comparison with the present invention. The RHF of Nakornthai Strip Mill Company Ltd. (NSM), in Thailand is of 45 meters (O.D.) with a hearth width of 6.5 meters to given an annual capacity in the range of 300,000 to 500,000 totals of direct reduced iron (DRI) on the total hearth area of 800 m.sup.2, depending on the degree of metallization of products. It is designed to have one or two layers of pellets containing carbonaceous reductant on the rotating hearth with heat provided by a flame. Near the end of one revolution, DRI is discharged with a screw discharger.
Use of an RHF for reduction of metal oxides at the present time has the following shortcomings:
(A) Less efficient use of land because the space inside the rotary hearth is of essentially the same area as that of the hearth. PA0 (B) High speed of the rolling stock. The linear speed of the rotating hearth increases with the increase of the diameter of the RHF, and limits the size of each unit. PA0 (C) The discharging operation: Higher linear speed of hearth movement and wider width of the hearth will lead to increasingly demanding operation of the screw discharger. PA0 (D) Servicing of any part of the hearth of an RHF necessitates shutdown of the whole unit and cooling to a low temperature. This lowers production per unit and shortens the service life of the furnace lining due to temperature changes.